The invention relates to a measuring probe for taking gas samples and/or making temperature measurements in furnace charges that are hot and have gas flowing through them, comprising a measuring head that can be moved along in a sampling tube.
A measuring probe of this kind is known from German patent specification 1 408 098: it is useful for taking gas samples and temperature measurements in shaft furnaces, especially blast furnaces, and consists of a sampling tube which can be moved horizontally and has a sampling passage axially through it along which a hollow rod with a thermocouple can be moved. Spaced from the tip of the thermocouple the hollow rod has an annular collar having an external diameter substantially that of the, internal diameter of the sampling passage. By pushing the hollow rod along the tube, the tip of the thermocouple can be made to emerge into the ore burden filling the furnace shaft and the sampling passage simultaneously opened, so that gas can be sucked out at the same time as the temperature of the gas or of the interior of the furnace is measured.
Such measuring probes are subjected to severe mechanical stresses, since a force of as much as 70 tons is needed to introduce them horizontally into the coke, ore, pellets, sinter and scrap making up the furnace burden. The measuring head or the front end of the lance must withstand the corresponding surface pressure, and in addition is subjected to particularly high stress when it is moved out of the probe or its sampling tube to make a measurement, as it is then surrounded on all sides by the furnace burden and by the hot flowing furnace gases. The probe and the measuring head are subjected to high bending forces and severe wear and tear both by the descending furnace burden and by the dust contained in the gas, which acts as a sand blast because of its high velocity. In addition there is the danger of caking on, especially of alkalis, and the danger of hot corrosion by the reducing furnace gas, containing inter alia alkalis, hydrogen, hydrocarbons, sulphur dioxide and metal oxides.
Although the known measuring probe has proved satisfactory, especially in blast furnaces, it has reached the limit of its utility in present-day blast furnace operation on account of increasing furnace temperatures due to the blowing in of oil and coal dust and the resulting extremely high stresses, since the measuring head needs to have high strength and resistance in all respects, as otherwise it cannot be pushed along in the sampling passage. In particular it must not be subject to distortion or scaling and formation of deposits, as otherwise the measuring head will jam in the sampling passage and block the gas passage.
Attempts to improve the cooling of the sampling tube and/or the measuring head to make introduction at higher operating temperatures possible have been unsuccessful, since the associated greater removal of heat cannot but influence the surroundings of the measuring head and/or the results of the measurements.
As a result of this the temperature at which conventional measuring probes can be used is limited to about 1100.degree. C. In addition the more frequent replacement of the measuring head, made necessary by increasingly high temperatures, requires the measuring probe to be withdrawn each time from the pressurised furnace and the new one to be introduced into the furnace or the furnace charge. Because of the high temperature and the pressure in the furnace, this requires considerable effort and exposure to danger on the part of the operating team.